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The other day I was installing some low voltage under-cabinet strip lighting in the kitchen and I had another opportunity to use the Milwaukee M12 soldering iron.

A portable soldering iron isn’t a tool I use every day or even every week. When I have serious soldering to do I, usually fire up my Metcal station at my workbench. If I have to take my soldering on the road so to speak, I’ve previously used an old Radio Shack butane soldering iron. While it is smaller and lighter, the biggest problem I have is that it’s hard to light.

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Since I received the M12 cordless soldering iron sample from Milwaukee, when I need to solder away from my bench, I’ve been trying to use it, instead of my butane iron.

You can purchase the M12 soldering iron as either a bare tool (2488-21) for $69, or in a kit (2488-21) for $129 with a charger, 1.5Ah battery, and case. Both versions include the chisel and conical tips.

Heat Output

When I saw the Milwaukee cordless soldering iron at NPS17, my first question to the presenter was, “can it solder a penny?” This was a trick that an old engineer I studied under showed me. If the soldering iron you were trying to sell him couldn’t do this, he wasn’t interested.

Why is this relevant? Because you don’t melt the solder with the tip of the iron, you heat the material until it is hot enough that it melts the solder. Sometimes you need to solder to a large wire or ground plane. Surfaces like that can soak up the heat faster than the iron can keep up.

Of course nobody at the NPS show had a penny I could try to solder, and so this was one of the first things I tried when I received a test sample of the M12 soldering iron.

It took about 30 seconds to get the penny hot enough to melt the solder. I posted the video to Instagram last November 2017.

Stability

With a bench soldering iron, you have a dedicated stand that you return the iron to when you aren’t using it. Portable soldering irons have to be set down in uncontrolled environments. Some portable irons have a built in stand, but that’s just one more thing to get in the way.

The M12 soldering iron doesn’t need any sort of stand, as it is pretty stable in all of its configurations. As long as you put it down on a level surface, the hot tip won’t contact the surface.

Something I found useful in some cases was to use a 6-cell XC battery. Not only did it extend the run time considerably, but the 6-cell M12 batteries provide a really stable base. The only disadvantage is that it adds half a pound to the weight of an already heavy soldering iron.

Use Cases

That brings me back to installing the under-cabinet lighting. I wanted the installation to be invisible when you are standing at the counters. I couldn’t run a continuous LED strip because the lighting was going under three different cabinets. So I needed to cut three different strips, and connect them with wire fished through holes in the bottom of the cabinets.

There was really no way I could pre-assemble the strips. I suppose I could have used connectors, but that would have required drilling larger holes through the cabinets.

Connecting the strips together required me to get on my back on the counter top and solder above my head.

Above you can see a closeup of the strips and solder joints. They aren’t my prettiest work, but they are sound solder joints.

In this case, even though the M12 soldering iron is bulky, it worked pretty well. When I wasn’t using the iron, I was able to put it down safely and pick it up again without looking because I wasn’t afraid it was going to tip over and burn something.

Besides soldering wires, I’ve tried soldering components on printed circuit boards. Above is an example at one such attempt. I blew out the fuse on an M12 power source. You can see it in the lower right (marked TN). You can also see my attempt to solder the new fuse back in place with the M12 soldering iron – not my greatest work again.

To be fair, Milwaukee designed their M12 cordless soldering iron for automotive installers, field techs, and other such users. It’s more meant for soldering wires than small components like surface-mounted fuses.

With the bulky iron, I found it really awkward to position the tip of soldering iron on the component pads where it needed to be.

And no, I didn’t touch those other resistors and capacitors, that’s how I found them. It almost looks like this board was hand soldered.

Final Thoughts

Would I recommend the M12 soldering iron? The answer is it depends. I find it easier to use than a butane soldering iron. You don’t have to worry about burning something when you put it down, and it gets the job done just as well.

A smaller butane iron is cheaper, smaller, and more maneuverable, but if you are in the field quite a bit, you are already in the M12 system, and you don’t mind the large size, this soldering iron might be a good fit.

This soldering iron is definitely not a replacement for a desktop soldering iron. Instead, it’s what you can take where a traditional soldering station cannot go.

Bonus Content

Here’s a thermal image of the tip after the iron has been powered on for about 5 minutes. The tip temperature isn’t accurate, but you can see which areas heat up relative to others. The tool itself remains pretty cool.

I tested the tip temperature with a thermocouple and measured it to be 735°F.

There could be a few reasons I didn’t get up to 750°F. First, I wiped the tip dry of solder because I was afraid of ruining the thermocouple, but the liquid solder might be necessary for proper heat transfer. Second, the thermocouple might be a few degrees off. Finally, Milwaukee might have been a little generous specifying a 750°F max temp. I’m not going to be too critical though, because I measured within 2% of their stated max temperature.

I was really excited when somebody told me that the Hakko T18 tips might be compatible with the M12 soldering iron, as this would open it up to a huge variety of tip sizes and styles that you could use for different applications.

But, I discovered that they were just different enough that they didn’t completely come in contact with the flair on the shaft. It turns out they are still usable, but I wouldn’t recommend them, because you might damage the heating element.

About Benjamen

Benjamen Johnson grew up watching his dad work as a contractor and woodworker. He became an electrical engineer and took an interest in woodworking. Check out Ben's projects at Ben's Workshop or follow him on twitter or instagram.

19 Comments

A buddy of mine bought one of these so I’ve seen it and held it. It’s ENORMOUS for a pencil iron. 90 watts is a decent amount of power and is indeed has a lot of thermal reserve, but 750° is too hot for many tasks. This thing needs a temperature adjustment, at least. Most of my soldering is at 640° which with a 90 watt heater behind it is plenty for even #12 wire.

If you’re working on trailer wiring this might be about the right size. For your LED tape project it was too big and too hot. For general use, get a Hakko FX-888, or get a modern butane like the Portasol P2KC.

I like mine. Only complaint is the led leaves a shadow on the exact spot you’re trying to solder which actually makes this point seem darker, not more visible. But that’s a minor complaint. Overall it’s been a winner for me.

The tip temp is regulated, otherwise I wouldn’t have been able to solder the penny. I’m not sure or the actual circuit, but I believe it’s a resistive heating element so you can monitor the resistance and measure the temp. You can do it actively or have a circuit that compensates automatically.

There are several ways you could modify the iron. You could change the position of the heating element or just add a spacer. I just don’t want to officially recommend it.

With the size of the iron. I figured a bent conical tip would have been perfect to reach in for PCB work.

I’ll probably end up needing this soon on a upcoming project that will be my excuse to need one lol. I do like your light install, i can’t wait to do that on my cabinets when i finally get my house built.
My m12 3/8 impact wrench will be here on tuesday! Much Excitement! Then acme tool, tool nut, and international tool are accepting pre-orders for the m12 rocket light that comes out next month… I haven’t pulled the trigger yet but it’s going to be very hard not to now that i have a couple extra m12 batteries.

I preordered mine last year and have only used it a couple of times. That said, Benjamin, your review is really appreciated. I’m always trying to anticipate my “tool” needs and this still seems like an easy to rationalize M12 investment. (My wife would say “too easy”)…
Thanks for the great review.

Oh. The M18 heat gun with the optional nose piece set has proven more handy as we use shrink tubing a fair amount.
It doesn’t heat up as fast as plug in versions for sure but once it does there are no wires let alone line power requirements.
Lord knows what its exact heat output actually is but it does slowly but surely get its job down. Use at least a 5Ahr battery since weight and balance aren’t very critical. Certainly not as much as the M12 soldering “pencil”.

I had the exact same problem with Hakko tips being too short and Milwaukee only having the 2 tip types. I had major issues finding replacement tips in different profiles, I spent more than a month looking and trying at different electronics stores and ordering/returning stuff online. I couldn’t find anything that worked.

Well, I finally found some. They are Hakko 900M style tips (the version before the T18, and these are not Hakko brand). I wish I could find a set in the US, but no luck so far. I have a set of these and tried them out last week. They fit correctly, and solder correctly. I can’t speak to durability, since I have only used them for about a week. For 25 cents each, I’m not sure if I care if they don’t last a while.

I wish they would have made a smaller iron connected to a base, that was battery powered, instead of the huge completely cordless unit. Or maybe have the charger also act as the power supply when not plugged into the wall. It would seem much more versatile that way to me.

I’m glad they came up with this, but I”m quite happy with my butane iron that cost about $20 and fits in a shirt pocket. The small size makes it more maneuverable in tight spots, as well. Most of my uses end up being in tight spots, something to consider.